1. Field of the Invention
This invention relates to the monitoring of processing apparatus and more particularly to methods of and apparatus for monitoring for conditions indicative of displacement of an electrode in a molten body of heat softenable material and of incipient electrode or refractory wall failure in a heating and melting apparatus for Joule effect heated heat softenable material.
2. Description of the Prior Art
The electrical heating of heat softenable materials by Joule effect involves establishing electrical current communication with the material through electrodes. A typical heat softenable material, glass, has been maintained at or above the usual working temperatures, about 2600.degree. F, by immersing one or more pairs of electrodes in the molten glass and passing controlled pulses of electrical power from the electrodes through the glass. Frequently these electrodes have substantial portions of their glass contacting surfaces spaced from the walls of the container or furnace for the glass to reduce the heat imposed on those walls and extend wall life. One electrode form involves a right circular cylinder which is extended vetically through the bottom of the furnace. Although a number of expedients are employed to protect the electrode and the bottom refractory, it has been found that there is a tendency for electrodes to erode in the region of the wall through which they pass and to slump from a vertical orientation.
In the case of the cylindrical electrodes cooling jackets have been mounted around the electrodes beneath the furnace bottom to reduce the electrode temperature external of the furnace to a level at which it is not subject to attack by constituents of the atmosphere. Further, it is not uncommon to maintain an inert atmosphere within the jacket and around the electrode so it is protected in the portion of its length in which the temperature approaches that within the furnace. Even with such precautions electrodes tend to erode, usually in the region of and slightly below the furnace floor-molten glass interface. Such erosion can result in the breaking off of the electrode in the melt.
Upon breaking an electrode, the furnace wall in the vicinity of the remaining stub portion is attacked and will develop leaks unless corrective action is taken promptly.
In the aforenoted related applications changes in the cross sectional area of an electrode as by a necking down of the electrode and the creation of fractures in the necked region were taught to result in characteristic changes in the electrical parameters for the electrodes which could be monitored and, at threshold levels, actuate indicators.
Recently, it has been observed that Joule effect heated glass melting tanks can be punctured by the slumping of electrodes mounted to extend vertically through the furnace bottom. These punctures are attributed to electrical, physical and thermal erosion of the refractory furnace bottom wall by the slumped electrodes. The nature of the slumping influences the detrimental effects on the furnace operation since in some conditions adjacent electrodes can slump to produce an effective short circuit between them. It has also been observed that the electrodes which are continued in operation after they have slumped tend to be eroded to a cut-off state in the vicinity of the bend from the desired vertical orientation. thus it is desirable to detect the slumping of electrodes in the opaque mass of the thermally softenable material in order to establish corrective procedures or avoid the undesired consequences of continuing the mode of operation then in effect.